Hey all,

I have a quick question. I am a fairly new owner (1 week) of an '89 IROC-Z with everyone's favorite engine, the 305 TBI (; I am having a new 305 installed this week. Old one has 180,000 miles. Either way, one of the mods that I would like to do is replace the throttle body with a larger one. As new as I am to this, I am not sure of the limitations of the throttle body size. BBK has one at 52mm and one at 58mm. Would both sizes work, and if so, how much of an improvement would there be on a stock engine, if any? Or am I thinking about this all wrong and need a good mental adjustment for even asking this? Any input is appreciated.

Thanks,
Andy

 

Those Throttle Bodies are for TPI and LT1 cars only. A TBI car has a different throttle body. The stock size is 1 11/16" each which works out to be around 42.8mm each butterfly. You can take your throttle body to a machine shop and have them bore it to a max of 48mm each, which is plenty for a stock, or mildly modded 305. I plan on having mine bored myself.

Clint

 

That helps. Thanks for enlightening me. Any idea what kind of performance to expect with a bored throttle body on a stock engine?

 

Unfortunately, Not the slightest idea. You may have to bore out the stock intake as well to see any real difference, because they are the same size as the stock TB. You will see the best difference after freeing up your exhaust, installing an LT1 cam, and swapping in a carb intake with an adapter plate, and some new heads, but that takes some money.

If you want to see some more power out of your car, start with your exhaust, as it has to breath out, before it can breath more in. A good 3" catback exhaust, 3" cat, and a set of decent headers, will really help to get you started.

Clint

 

http://www.turbocity.com/TBIPowerMain.htm

 

That's awsome guys! Thanks. Looks like in the next few months we'll see a new catback system and a bored out TBI. Just don't tell my wife. Just gonna have to tell her that my injectors are clogged and need to be replaced and my exhaust fell off on Rt 75.

Thanks,
Andy

 

lol thats funny ur wife...... im having the same issues with my mom...... seems like u never get away from it... damn heh lol